Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $119.83   8.706%   $130.2624   $130.26   $130.25   $130.30  
  Purchase #2 $230.74   6.820%   $246.4765   $246.48   $246.50   $246.50  
  Purchase #3 $74.75   3.224%   $77.1599   $77.16   $77.15   $77.20  
  Purchase #4 $54.32   11.619%   $60.6314   $60.63   $60.65   $60.60  
  Purchase #5 $167.70   6.156%   $178.0236   $178.02   $178.00   $178.00  
  Purchase #6 $25.36   10.292%   $27.9701   $27.97   $27.95   $28.00  
  Purchase #7 $162.97   7.538%   $175.2547   $175.25   $175.25   $175.30  
  7 purchase totals = $835.67       $895.7786   $895.77   $895.75   $895.90